1. Field of the Invention
The present invention relates to an improved sealing apparatus for accomplishing heat sealing of a medication blister card including unit doses of medication in the blisters. The improved apparatus of this invention is characterized by its construction including a card holder which receives the filled medication card and a heated sealing head which is movable into juxtaposition with the exposed top surface of the medication blister card to sandwich the card between the sealing head and the card holder while applying both heat and pressure thereto to accomplish the sealing operation. The card holder comprises a plurality of first ridges formed substantially around the perimeter thereof and a plurality of second ridges formed thereon around the perimeter of each blister of the medication card. The sealing head comprises a knurled surface which actually contacts the exposed top surface of the filled medication card during the sealing operation. Thus, during the sealing operation, the medication blister card is "sandwiched" between the card holder and the heated sealing head. The first and second ridges formed on the card holder extend upwardly from the surface of the card holder and, during the sealing operation, effectively define channels whereby moisture driven from the card as the result of application of pressure and heat from the sealing head may condense on the main surface of the card holder. This condensation is significant for at least two reasons. First, because the moisture condenses on the card holder, the moisture may be said to be driven away from the medication blister card. Obviously, one would not wish moisture to collect within the individual blisters, for that could easily result in deterioration of the medication contained therein. Second, the condensation effectively cools the card holder during extended periods of operation of the apparatus. This cooling effect is significant for the reason that the blisters of the medication blister card are almost without exception formed from a plastic material. Should the card holder become excessively hot, that heat could have an adverse effect not only upon the blisters, but also upon medication contained therein. It should also be noted that the provision of first and second ridges as well as construction of the contact surface of the sealing head to include knurling also enhance the physical integrity of the overall seal of the card.
2. Description of the Prior Art
Within the medical service profession, it often occurs that a particular patient is to receive a unit dose of medication at regularly occurring intervals such as, for example, once a day. Both the purposes of insuring that medication is properly administered and taken, as well as for maintaining effective cost control, it is quite common to administer such regularly repeating doses of medication by packaging the medication in medication blister cards containing individually sealed doses. Such cards are frequently referred to within the profession as "bingo cards."
Just as the use of such medication blister cards for packaging unit does of solid or substantially solid medication is quite common, so are inherent difficulties associated with the preparation of such cards. A first problem encountered within the profession concerns efficient means for placing the medication within the individual blisters, and a variety of devices and means are available for that purpose. A second problem concerns the actual sealing of the filled cards. The main components of standard medication blister cards are top and bottom sheets of cardboard hinged together as by a fold. Both of the cardboard substrates include apertures formed therethrough corresponding to the individual blisters. One of the cardboard substrates generally includes an aluminum foil placed on the interior surface thereof in closing relation to the blister apertures. The other cardboard substrate normally includes a blister sheet formed from plastic and defining a plurality of blisters corresponding to the apertures placed thereon. Thus, when the individual apertures are filled while the card is open, the card may then be folded onto itself so that the foil-cardboard sheet closes the blister-cardboard sheet. The card is then sealed by the application of pressure and heat. It is with particular regard to this sealing operation that difficulties may arise.
First, because medication is contained in the card, it is extremel important that the physical integrity of the sealed card be maintained. Second, because the cards primarily comprise cardboard stock, it is well known that the empty cards will absorb significant quantities of moisture during transportation and storage. Since the sealing operation, almost without exception, is accomplished by pressure and heat, moisture is driven from the card. In many instances this mean that moisture actually condenses on the inside of the individual plastic blisters. This is quite obviously not desirable, for moisture will rapidly deteriorate many forms of medication. Furthermore, because the sealing process generally involves the application of heat at temperatures of 400.degree. F. or higher, care must be taken to insure that this heat is not transferred to the plastic blisters or to medication contained within the blisters. Transfer of heat to medication is particularly troublesome when the medication is of a gelatinous form.
Of course, heat seals, per se, are quite old and well known. It is therefore not surprising that numerous means are taught in the prior art for accomplishing such heat seals. For example, U.S. Pat. No 2,768,272 to Lesher teaches that a heat source having a knurled contact surface is useful for heat sealing thermoplastic material. Another thermoplastic welding or sealing device is disclosed in U.S. Pat. No. 2,963,072 to Swartz. That patent teaches the application of sealing heat through what might accurately be described as a tongue and groove holder for the materials being bonded together. A somewhat similar land and groove apparatus is disclosed in U.S. Pat. No. 4,001,075 to Menzner. Though not strictly a sealing apparatus, U.S. Pat. No. 4,243,470 to Higashiguchi teaches a device for applying heat transfers. A fixed base plate is provided and the material onto which the heat transfer is to be applied as well as the heat transfer itself are held between that base plate and a movable heat plate. According to the teaching of this patent, more efficient transfer takes place when either the base plate of the heat plate comprises a plurality of holding means defined by needles extending toward the material onto which the transfer is to be placed. It is quite apparent that the utilization of such needles would be totally inappropriate with regard to the sealing of medication cards, for the needles would destroy the physical integrity of the individual blisters of the card. Finally, U.S. Pat. No. 4,398,883 to Vetter, et al. discloses a packaging machine wherein the contacting surface of the heating plate includes a plurality of raised zones surrounded by interconnected retracted zones to prevent the inclusion of any residual air between the thermoplastic packaging foil and the contacting surface of the heating plate.
Thus, while it certainly cannot be denied that the prior art teaches a variety of devices which might be used for sealing medication blister cards, there is no teaching nor suggestion in the prior art of a sealing apparatus including means for channeling absorbed moisture from the card and away from the medication blisters, and also including means for reducing the likelihood of heat damage to the plastic blisters or medication contained therein. It is therefore clear that there is a great need in the art for a simple, yet efficient and economical, means for sealing medication blister cards while at the same time substantially reducing, if not eliminating, adverse affects to the card and its medication relating to moisture condensation and heat build-up. Furthermore, it would also be desirable if such an apparatus could easily be utilized for sealing medication blister cards of a variety of sizes and configurations.